The present invention relates to a magnetic disk apparatus, and more specifically to a magnetic disk apparatus provided with a carriage lock mechanism.
Recently, magnetic disk apparatuses provided with a magnetic head of a so-called CSS (contact start-stop) type have been used in which the magnetic head is in contact with a head landing zone of a magnetic disk while the apparatus is nonoperating. In the magnetic disk apparatuses of this type, the magnetic head and magnetic disk are very susceptible to vibration and impact. When the apparatus is nonoperating, therefore, it is necessary to lock the magnetic head, thereby minimizing damage attributed to vibration or impact.
Conventionally, the magnetic head is locked at a predetermined position by manually operating a lock lever when the apparatus' power supply is cut off. According to this method, although the possibility of damage to the magnetic head or magnetic disk may be reduced in some measure, it is necessary to lock or unlock the magnetic head by operating the lock lever each time the apparatus is switched on or off, resulting in a complicated operation.
According to an alternative conventional method, the magnetic head is locked by means of a solenoid.
In general, the magnetic head is fixed on a carriage which is movably disposed on a base frame. The carriage is movable between a stop position where the magnetic head is located on the head landing zone of the magnetic disk and a position remote from the stop position. The carriage is normally urged toward the stop position by a return spring. A driving coil is fixed to the carriage, and a magnet is fixed on the base frame, adjoining the coil. When the driving coil is energized, the carriage is driven in a predetermined direction by the joint action of the magnet.
Meanwhile, the solenoid is fixed on the base frame, and its plunger is connected with a lock lever which is rockably mounted on the base frame. The lock lever is adapted to engage a retaining portion formed on the carriage when the carriage is rocked to the stop position. A lock spring is connected to the lock lever, whereby the lock lever is urged to engage the retaining portion of the carriage.
According to the magnetic disk apparatus constructed in this manner, during operation or while the power is on, the solenoid is energized to attract the plunger, so that the plunger causes the lock lever to move away from the retaining portion of the carriage against the urging force of the lock spring. As a result, the carriage is unlocked. Also, the driving coil is energized, so that the carriage is moved to a desired position against the urging force of the return spring. When the apparatus is switched off after the operation is ended, the solenoid is deenergized, and the carriage is returned to the stop position by the return spring. Thus, the retaining portion of the carriage and the lock lever frictionally engage each other, so that the carriage is locked to the stop position by the lock lever.
In order to securely lock the carriage to the stop position in this apparatus, it is desired that the lock lever is rocked to engage the retaining portion of the carriage after the carriage is fully moved to the stop position. In this apparatus, however, the lock lever and the retaining portion may sometimes engage each other before the carriage reaches the stop position. According to the apparatus of this type, therefore, the urging force of the return spring is made greater than that of the lock spring so that the lock lever can be pushed back by the retaining portion even if the lock lever and the retaining portion engage before the carriage is moved to the stop position. In this case, however, the retaining portion and the lock lever would rub against each other and wear, producing chips. These chips may stick as dust to the magnetic head and magnetic disk, possibly damaging the same. In order to securely hold the carriage in its stop position, moreover, the lock spring should preferably be made stronger. As mentioned before, however, the urging force of the return spring must be greater than that of the lock spring. If the urging force of the return spring is great, a lot of power is needed to drive the carriage. This necessitates the use of a large magnet and a large driving coil, resulting in an increase in the size and manufacturing cost of the apparatus. Also, the action of the carriage is liable to lag.